• Coronary collateral circulation continues to be a poorly understood phenomenon.
• It reduces the impact  of ischemia , salvage myocardium, keep it viable, and  can  even  be  life saving during a STEMI
• It can support either the same coronary artery  or the contra lateral coronary artery (Like the above patient )
• The usefulness of  collaterals  at times of exertion is controversial .Most interventionists do not believe in  it . (Facts are opposite of course !)
• Bridging coronary  arterial collateral often indicate hardened total occlusion and success of  PCI is reduced

Here is  the  angiogram  which shows classical intra coronary bridging  collaterals.